Typical silicate phosphors used in fluorescent lighting applications include BaSi.sub.2 O.sub.5 :Pb, Zn.sub.2 SiO.sub.4 :Mn and CaSiO.sub.3 :Pb,Mn. Of particular interest is BaSi.sub.2 O.sub.5 :Pb which is used as the long-wavelength UV (347 nm) phosphor in fluorescent suntanning lamps. Its preparation and use have been described in U.S. Pat. Nos. 2,597,631, 3,043,781, and 5,234,625 which are incorporated herein by reference. A well-known drawback to the use of this phosphor, and silicate phosphors in general, is that lumen maintenance in fluorescent lamps is poor relative to other fluorescent lamp phosphors. That is, fluorescent lamps employing silicate phosphors exhibit a relatively rapid decrease in brightness over time.
It has been demonstrated, however, that the life of silicate phosphors can be extended considerably by applying a protective coating to the phosphor particles. In particular, U.S. Pat. Nos. 5,223,341 and 4,710,674 describe an A.sub.2 O.sub.3 coating which improves the maintenance of silicate phosphors in fluorescent lamps. The protective alumina coating is applied via a CVD method in a fluidized bed using pyrophoric organometallic compounds. While effective, the prior art method requires relatively complex coating equipment and hazardous chemicals. Thus, it would be advantageous to have a simpler, more economical method for protecting silicate phosphors and improving their maintenance in fluorescent lamps.